Non-thermal Plasma Catalysis Research Articles

Efficient removal of tetracycline antibiotic by nonthermal plasma-catalysis combination process

This study presents an innovative approach to plasma catalysis by employing nonthermal plasma type gliding arc with various iron oxides -Fe(II), Fe(III) and Ferrate Fe(VI)- for the removal of tetracycline antibiotic (TC). The experimental results demonstrated significant improvements in degradation rates, with plasma-Fe(VI) achieving complete degradation after 15 min of treatment and the plasma-Fe(II) achieving 97.28% removal after 30 min. The effect of TC initial concentration and catalyst dose was investigated, revealing that lower TC concentration favored the degradation and shortened treatment times with even a minimum amount of catalyst doses enhancing degradation results. Higher total organic carbon (TOC) removal was achieved in the combination systems (83.01%; 82.07%; and 42.82% for plasma/Fe(VI); plasma/Fe(II); and plasma /Fe(III) respectively) compared to plasma alone barely achieved 25.67% of mineralization. Additionally, the study examined the role of various radical scavengers-targeting <sup>•</sup>OH, superoxide, and free electrons- in the degradation process. TC intermediates were also identified, degradation pathways were proposed, and the intermediates toxicity was assessed. This research contributes to a deeper understanding of organic compounds treatment using nonthermal plasma, combination with the ferrate process or other catalysts.

Plasma Catalysis for Hydrogen Production: A Bright Future for Decarbonization.

Thermal approaches have played a dominant role in driving chemical reactions within the chemicals and fuels industries, benefiting from ongoing enhancements in efficiency via heat integration, catalyst development, and process intensification. Nevertheless, these traditional thermal approaches remain heavily reliant on fossil fuels, and there exists an urgent demand for the implementation of renewable energy technologies to synthesize fuels, commodity chemicals, and specialty chemicals. Nonthermal plasmas have gained considerable attention in recent years as a promising solution, and the prospects of combining plasmas with suitable catalysts have become even more appealing. Moreover, the evolution of nonthermal plasma catalysis approaches for the generation of clean hydrogen could be transformative in reducing greenhouse gas emissions. This comprehensive review highlights the influential contributions in plasma catalysis for hydrogen production, discusses recent advancements, and provides future prospects for researchers aiming to advance the production of clean hydrogen.

Plasma-catalytic CO2 methanation over Ni supported on MCM-41 catalysts: Effect of metal dispersion and process optimization

Catalytic carbon dioxide (CO2) conversion technologies can be important components in carbon capture, storage and utilization for CO2 mitigation and possible future economic activity and have gained significant attention globally in past decades. Electrified non-thermal plasma (NTP) catalysis enables CO2 hydrogenation into value-added chemicals under mild conditions. If the hybrid process is coupled with renewable energy and green hydrogen, it can be the promising solution to address the energy and carbon emission challenges. To enhance the energy efficiency of NTP-catalytic systems, bespoke catalyst design and process optimization are necessary. Here, using Ni catalysts supported on mesoporous MCM-41 and NTP-catalytic CO2 methanation as the model systems, the effects of Ni metal dispersion, argon (Ar) addition and residence time on the NTP catalysis were also studied. The findings show that (i) increased metal dispersion alone did not lead to significant enhancement in the performance of NTP catalysis (e.g., CH4 production rate: 31.4 × 10−5 mol/(s·gNi) for 42.6 % Ni dispersion vs. 26.8 × 10−5 mol/(s·gNi) for 25.1 % dispersion), (ii) Ar addition to the system led to the decreased methane production rate (e.g., CH4 selectivity decreased by ∼19 % due to the increase in Ar addition to the system from 5 to 50 mL/min), and (iii) optimization of the residence time could improve the performance of NTP-catalytic CO2 methanation (i.e., an extension of the residence time to 0.69 s resulted in the higher CO2 conversion of 72.7 % and CH4 selectivity of 95.9 % at 9.6 kV than that at 0.49 s and 11 kV).

Catalytic non-thermal plasma reactor operating at low applied voltage for the removal of toluene in air

Volatile organic compounds (VOC) represent a large group of pollutants characterized by high volatility. They can cause problems both for humans and the environment. This work aimed to examine the non-thermal plasma (NTP) technology combined with a heterogeneous catalyst (“in plasma catalysis”, IPC) for the removal of toluene from the air at an applied voltage lower than that commonly reported in the literature. The NTP system was studied in the absence and presence of two commercial catalysts (γ-Al2O3 spheres and TiO2 pellets) investigating the influence of the operating conditions (inlet flow rate, inlet pollutant concentration, water vapor presence and applied voltage). The results demonstrated that NTP without catalyst can remove toluene at voltages not less than 13.20 kV. On the other hand, the use γ-Al2O3 in IPC configuration allowed to achieve better performance than TiO2 with the lowest applied voltage (10.67 kV) for plasma generation. Specifically, with an air flow rate of 15 NL/h at 8.7% of relative humidity and containing 500 ppm of toluene, a pollutant conversion of about 89% and a CO2/CO molar ratio equal to 4.72 was achieved. Moreover, contrary to what was observed in the NTP system without catalyst, the presence of both γ-Al2O3 and TiO2 in the IPC configuration allowed to avoid the presence of O3 and NOx at the reactor outlet. Finally, the calculated energy efficiency was in the order NTP+ γ-Al2O3 > NTP+TiO2 > NTP alone.

Regulating electronic metal-support interaction (EMSI) via pore-confinement to enhance non-thermal plasma catalytic oxidation of toluene

The non-thermal plasma catalysis holds great promise for VOCs removal, and the development of catalysts with electronic metal-support interaction (EMSI) effect is beneficial for VOCs removal. In this study, we prepared three Mn@M catalysts with EMSI coordination structures by encapsulating MnOx particles within the mesoporous molecular sieve (MCM-41) with different pore size (2.9 nm, 4.4 nm, and 7.9 nm), and investigated the effect of pore size on EMSI and non-thermal plasma catalytic performance of Mn@M for toluene. Among three catalysts, Mn@M2 with an average pore size of 4.38 nm exhibited the strongest EMSI and superior redox capabilities, thus demonstrating the highest mineralization rate, carbon balance, and CO2 selectivity for plasma catalytic oxidation of toluene. The EMSI effect leads to the formation of electron-rich and electron-poor centers on the Si-O-Mn-O bond, facilitating the generation of reactive oxygen species and enhancing the oxygen cycle. In addition, the reaction degradation pathway was investigated using in situ DRIFTS and GC–MS. This study provides valuable insights for designing highly effective supported catalysts by pore confinement to degrade VOCs in adsorption-plasma catalysis system.

Non-thermal plasma catalysis driven sustainable pyrolysis oil upgrading to jet fuel under near-ambient conditions

The integration of non-thermal plasma with a nanoclustered Ir catalyst achieves an 87% liquid oil yield from pyrolysis oil, showcasing the transformative impact of plasma-catalysis synergies in activating methane and cleaving long-chain oil molecules.

Methanol steam reforming for hydrogen production over Ni/ZrO2 catalyst: Comparison of thermal and non-thermal plasma catalysis

Hydrogen (H2) is the promising clean energy which can contribute to the achievement of the Net Zero goals. Herein, the Ni/ZrO2 catalyst was developed for methanol steam reforming for H2 production. The catalyst possesses the features of good redox property, and the presence of surface chemisorbed oxygen, and large specific surface area. The Ni/ZrO2 composite together with the control of NiO and ZrO2 were assessed by thermal and non-thermal plasma (NTP)-activated methanol steam reforming reactions, and the results showed that NTP itself was able to initiate methanol conversion, whilst the inclusion of the composite catalyst did not improve the reaction significantly, e.g., hydrogen production rate = 0.162 mmol·min−1 over Ni/ZrO2 under the plasma condition (at 90 ℃ and 9.4 kV). This could be attributed to the change of reaction pathways for methanol conversion in the presence of Ni/ZrO2 under the NTP condition, compared to the thermal systems employing Ni/ZrO2. Comparatively, the thermal catalytic system was not active at 90 °C regardless the catalysts used. At 400 °C, the Ni/ZrO2 catalyst showed satisfactory activity with a hydrogen production rate of 0.708 mmol·min−1. In addition, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and DFT calculations were performed to understand the relevant reaction mechanisms, revealing that methoxy and formic acid species were the key intermediates for methanol steam reforming.

Research on degradation mechanism of trichlorobenzene and Hg0 by nonthermal plasma catalysis

Aiming at mercury and dioxin in fire coal gas as research objects, nonthermal plasma (NTP) catalytic technology was used to investigate the degradation effect of operating condition parameters on mixed pollutants in mixed flue gas condition, and to explore the synergistic degradation of Hg0 and TCB (1, 2, 3-trichlorobenzene, TCB) under mixed flue gas conditions. The research results showed that the conversion efficiency of mercury and TCB increased with the additional output of voltage, and decreased with the increase of the gas flow rate. Under optimal reaction conditions: voltage = 17 kV, frequency = 300 Hz, gas flow rate = 2 l min−1, the conversion efficiency of Hg0 and TCB reached the highest 91.4% and 84.98%, respectively. In the NTP catalytic system, active free radicals played an important role in the synergistic conversion of mercury and TCB, which have a competitive effect, to make the conversion efficiency of mixed pollutants lower than a single substance. In the mixed flue gas condition, the mixed gas has an inhibitory effect on the synergistic conversion of mercury and TCB. Kinetic modeling of NTP catalytic synergistic reaction was established. Under three conditions of TCB, mercury and TCB, mixed simulated flue gas, the NTP catalytic technology showed a quasi-first-order kinetic reaction for the degradation of TCB. According to the synergistic effect of NTP and composites, the transformation and degradation of TCB mainly included two processes: TCB and ring opening, and Hg0 was finally oxidized to Hg2+.

Insights into plasma-catalytic nitrogen fixation from catalyst microanalysis and chemical kinetics modelling

Current industrial nitrogen fixation technology is unsustainable and has adverse environmental effects due to its reliance on fossil fuels. Using electricity-driven non-thermal plasma catalysis to fix nitrogen into NO3− is a promising solution, but the underlying mechanisms remain largely unknown. This study integrates a structured catalyst into a plasma column with a water-electrode bubble reactor that can fix nitrogen at ambient pressure and temperature with a 93% selectivity to NO3− with excellent catalytic stability. Characterizations of the catalyst and in situ plasma diagnostics indicate that the enhanced production of nitrate ions is due to abundant chemisorbed oxidized nitrogens species originating from NO and NO2 produced by the air plasma. The plasma chemistry model combined with DFT simulations demonstrates the role of structured TiO2 supported by 5% graphene oxide (GO) to improve NOx surface association while minimizing NOx backwards dissociation. The modelling results suggest the critical role of NO3(ad) in enhancing NOx production predominantly in the form of N2O5 molecule in the gas phase, resulting in efficient NO3−(aq) production as a final product in water. The study offers novel findings on plasma-catalyzed nitrogen fixation, advancing its potential for clean energy and eco-friendly chemical production through plasma-based power-to-chemical processes.

Basic metal oxide integrated DBD packed bed reactor for the decomposition of CO2

A coaxial dielectric barrier discharge (DBD) reactor was used to perform catalytic non-thermal plasma for CO2 conversion under ambient conditions. A systematic study was made to understand the role of basic oxides in activating weakly acidic CO2. For this purpose, MO/γ-Al2O3 (M = Mg, Ca, Sr, and Ba) catalysts were synthesized and integrated with the DBD reactor. The applied voltage was varied from 16 kV to 22 kV to determine the effect of applied voltage on CO2 conversion. Plasma discharge generates high-energy electrons that activate the basic oxides. Integration of basic metal oxides with the non-thermal plasma reactor resulted in a higher CO2 conversion. The adsorption of weakly acidic CO2 on the basic sites is responsible for the higher conversion of catalytic plasma reactor over plasma reactor alone. Among the basic metal oxides studied, SrO loaded γ-Al2O3 resulted in the best conversion, where CO2 conversion of ∼ 12% and energy efficiency of ∼ 1.46 mmol kJ−1 was attained at a power of 1.8 W. The concentration of O2 and O3 was measured during the reaction. The hybridized system's superior performance may be due to increased charge deposition and altered gas-phase chemistry because of catalyst integration. BOLSIG + software was used to compute the mean electron energies and electron energy distribution function for various packing conditions.

Nonthermal plasma catalysis using ferrites as an efficient catalyst for toluene degradation

Nonthermal plasma catalysis using ferrites as an efficient catalyst for toluene degradation

Rational design of catalysts for non-thermal plasma (NTP) catalysis: A reflective review

Non thermal plasma catalysis (NTP-catalysis) has shown the unique characteristics to enable many challenging chemical conversions under mild conditions. However, to date catalyst design with carefully consideration of the features of NTP activation was less achieved. In this reflective review, we revisited our previous research critically to comment on the rational and irrational aspects of these studies regarding catalyst design for selected NTP-catalytic systems, that is, CO2 methanation, dry reforming of methane with CO2, and NH3 synthesis. Additionally, comments on catalyst design in relation to relevant literature on the NTP-catalytic systems above, especially CO2 methanation, were also made. Based on that we devised relevant suggestion and prospect on rational design of bespoke catalysts for NTP-catalysis, which can be beneficial to advance NTP-catalysis technologies.

Sustainable ammonia synthesis from nitrogen wet with sea water by single-step plasma catalysis

Ammonia synthesis at ambient conditions employing intermittent distributed green sources of energy and feedstocks is globally sought to replace the centralized Haber-Bosch (H-B) process operating at high temperature and pressure. We report herein for the first time an effective and sustainable ammonia synthesis pathway from N2 wet with seawater vapor over spherical SiO2 and M/SiO2 (M: Ag, Cu, and Co) catalysts driven by non-thermal plasma (NTP). Experimental results indicate that the presence of a catalyst is required for ammonia production from seawater vapor and N2. The Co/SiO2 catalyst delivered the highest ammonia synthesis rate (rNH3) of 3.7 mmol gcat-1 h-1 and energy yield of 3.2 gNH3.kW−1.h−1 at a relatively low input power of 2 W. The extraction of H atoms from H2O molecules plays an important role in the ammonia synthesis from seawater vapor. This work unfolds a novel platform for the subsequent optimization of sustainable ammonia production from endless resources such as seawater and N2 through catalytic non-thermal plasma potentially powered by renewable sources.

Sustainable Hydrogen and Ammonia Technologies with Nonthermal Plasma Catalysis: Mechanistic Insights and Technoeconomic Analysis

The search for novel catalytic processes is essential to combat climate change by tapping into sustainable hydrogen technologies, which rely on low-carbon H2 production and efficient H2 storage for global transportation. Ammonia, which can function as a H2 carrier for later dehydrogenation in COx-free hydrogen production, is recognized as one of the key solutions. The utilization of nonthermal plasma to catalyze reactions is a plausible means of replacing CO2-polluting fossil-dependent thermal processes. In this perspective, we summarize currently explored mechanistic insights in the catalytic plasma reactions to evaluate their readiness for industrial applications and propose future research outlooks in plasma-driven hydrogen technologies, with a primary focus on ammonia reactions. Relevant reaction mechanisms and catalytic design in other reaction systems that involve hydrogen storage (e.g., CO2 hydrogenation, CO2 methanation) and hydrogen production (e.g., methane reforming) are also evaluated to supplement our primary discussion on ammonia synthesis and decomposition. We further discuss possible implications of using plasma catalysis from the perspective of energy efficiency in comparison to existing thermal-catalytic counterparts, wherein we include insights obtained from different reaction systems, catalyst design innovations, and reactor engineering. Herein, we present current research gaps and propose future research directions to achieve energy-efficient catalytic plasma hydrogen technologies.

Ru- and Rh-Based Catalysts for CO2 Methanation Assisted by Non-Thermal Plasma

The need to reduce the concentration of CO2 in the atmosphere is becoming increasingly necessary since it is considered the main factor responsible for climate change. Carbon Capture and Utilization (CCU) technology offers the opportunity to obtain a wide range of chemicals using this molecule as a raw material. In this work, the catalytic Non-Thermal Plasma (NTP)-assisted hydrogenation of CO2 to CH4 (methanation reaction) in a Dielectric Barrier Discharge (DBD) reactor was investigated. Four different Ru- and Rh-based catalysts were prepared starting from γ-Al2O3 spheres, characterized and tested in both thermal and NTP-assisted methanation under different operating conditions. The experimental tests evidenced the very positive effect of the NTP application on the catalytic performance, highlighting that for all the catalysts the same CO2 conversion was reached at a temperature 150 °C lower with respect to the conventional thermal reaction. Among the prepared catalysts, the bimetallic ones showed the best performance, reaching a CO2 conversion of 97% at about 180 °C with a lower energy consumption with respect to similar catalysts present in the literature.

Non-thermal plasma assisted catalytic water splitting for clean hydrogen production at near ambient conditions

The catalytic non-thermal plasma (NTP) reactors have been widely applied for various plasma-assisted reactions to improve performance owing to the existence of the synergistic effect between plasma and catalyst. Herein, for the first time, the catalytic NTP reactors were engaged for hydrogen production by water splitting to explore the catalyst role in performance improvement. A preliminary catalyst, Au/(TiO2/SBA-15) (SBA-15: Santa Barbara Amorphous-15), was used to conduct catalyst optimization by adjusting metal loading amount, TiO2 loading amount, catalyst support type and metal species. The optimized catalyst was with a formula of 0.2 wt.% Au/(10 wt.% TiO2/SBA-15) and its hydrogen production rate was high up to 1.03 mL min−1 with a 36.9% water conversion, which is 245% of the performance of the NTP reactor without catalyst packing. To explore the inherent factors affecting the catalyst performance, the surface properties of the catalysts, such as specific surface area, pore volume and water adsorption amount, were investigated and correlated with the catalyst performance. Based on these, a hypothetic reaction mechanism that emphasizes the importance of surface discharge is proposed and a catalyst design principle is drawn as a catalyst with large surface area and pore volume as well as a moderate H2O adsorption amount performs the best. In theory, chemical kinetics modelling of H2O/Ar plasma was conducted to figure out possible reaction pathways for hydrogen production. The application of catalyst in NTP-assisted water splitting presents a promising path for performance promotion.

Catalytic non-thermal plasma reactor for oxidative degradation of toluene present in low concentration

Toluene is a common solvent used in paints, pesticides, resins, etc. Although toluene is found in low concentrations in an indoor environment, long-term exposure to it is hazardous. This research aims to study toluene oxidation in a catalyst-packed dielectric barrier discharge (DBD) reactor designed to withstand high flow rates. The DBD reactor was packed with commercially available Al2O3 first and then with Mn and Co oxide-coated Al2O3. The surface modification of Al2O3 with transition metal oxides significantly improved the reactor's performance. At a power input of 20.3 W (equivalent to 13.0 J/l), MnO2/Al2O3 efficiently decomposed 50 ppm toluene (93%), and the corresponding CO2 selectivity was 57%. The in-situ breakdown of ozone, which leads to the formation of more reactive oxidants such as atomic oxygen, appears to make MnO2/Al2O3 better among the catalysts studied. The mean electron energies and the energy electron distribution function were calculated using the BOLSIG+ program.

Nonthermal plasma for capturing CO2 as a path to ecologically clean energy

One of the serious environmental problems of our time is the impact on global climate change of the atmospheric pollution processes with greenhouse gases. Carbon dioxide is the most significant component of the anthropogenic impact on the heat balance of the earth. Therefore, reducing the concentration of greenhouse gases in the atmosphere is becoming increasingly important. Non-thermal plasma technology is considered as an attractive alternative for converting greenhouse gases into syngas and other valuable chemicals at lower temperatures. Highly active species generated in such a plasma are favourable for both initiation and propagation of chemical reactions. The combined effect of plasma and heterogeneous catalysis for fuel production from CH4 reforming has attracted increasing attention. The coupling between plasma and catalyst become complex when the catalyst is placed directly in the plasma. Both chemical and physical properties of the plasma and catalyst can be changed by the presence of each other. In this paper we studied resent progress in non-thermal plasma-catalysis research for CO2 capturing application.

Mechanochemical Synthesis of Bimetallic NiCo Supported on a CeO2 Catalyst with Less Metal Loading for Non-Thermal Plasma Catalytic CO2 Hydrogenation

Non-thermal plasma (NTP) catalysis is a promising technology for CO2 valorization with renewable H2, in which catalyst design is one of the key aspects to progress the hybrid technology. Herein, bimetallic NiCo supported on CeO2 catalysts, that is, NiCo/CeO2, were developed with less metal loading of ∼2 wt % using mechanochemical synthesis for NTP-catalytic CO2 methanation. During the synthesis, different addition orders of Ni and Co precursors were investigated, and the results show that the NiCo1/CeO2-I catalyst (which was prepared by the simultaneous addition of Ni and Co precursors, protocol I) exhibited the highest CO2 conversion (∼60%) and CH4 selectivity/yield (∼80%/∼50%), whereas the NiCo1/CeO2-II and NiCo1/CeO2-III catalysts (prepared by sequential addition protocols of II and III) showed very poor catalytic performance. Characterization results suggested that in protocol I, Ni and Co prefer to alloy, and concentrated oxygen vacancies on the CeO2 surface and high surface basicity are retained as well. Such properties of NiCo1/CeO2-I were responsible for CO2 activation and hydrogenation under NTP conditions, which was explained by the proposed mechanisms.

Toward Ideal VOCs and Nanoparticle Emission Control Technology Using a Wet-Type Catalysis Nonthermal Plasma Reactor

Several exhaust gas regulations are being implemented to prevent the hazardous emissions of volatile organic compounds (VOCs) and particulate matter (PM) from paint and print factories. The VOCs generate photochemical oxidants and suspended PM, such as PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> , which has become a global environmental problem. We evaluate the catalytic nonthermal plasma (NTP) technique for controlling the emission of VOCs. The article proposes a wet-type catalysis plasma reactor to extend the treatment of water-soluble VOCs. Initial evaluation of the proposed technique involves simultaneous removal of nanoparticles along with individual VOCs, toluene, acetaldehyde, acetic acid, and ammonia, at a relatively high gas flow rate of 10 L/min. Further, pellets of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</i> -alumina and TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> spheres are employed in the NTP reactors for assessing their catalytic performance. We install an MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> catalytic reactor downstream of the plasma reactor for ozone removal. Simultaneous treatment of typical VOCs and nanoparticles using dry and wet-type catalytic NTP reactors shows that the wet-type reactor has superior average particle collection efficiency of 100%. However, the dry-type NTP with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α</i> -alumina shows a higher toluene removal efficiency of 91% compared to 73% in the wet type. Further, the respective removal efficiencies for acetaldehyde, acetic acid, and ammonia are 100%, 100%, and 95%. Notably, the toluene removal efficiency drops to 65% with the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> catalyst.